Update Scala toolchainizaion per @simuons in bazelbuild#1633

- Removes an extraneous `compiler_sources_repo` call.

- `scala_toolchains` will now _always_ create the main Scala toolchain
  repository (there's no longer an option to turn it off).

- Registers `@io_bazel_rules_scala_toolchains//...:all` in
  `scala_register_toolchains.

scala/private/macros/scala_repositories.bzl

@@ -191,11 +191,6 @@ def _setup_scala_compiler_sources(srcjars = {}):
         scala_versions = SCALA_VERSIONS,
     )
 
-    compiler_sources_repo(
-        name = "scala_compiler_sources",
-        scala_versions = SCALA_VERSIONS,
-    )
-
 def _artifact_ids(scala_version):
     return [
         "io_bazel_rules_scala_scala_library",

scala/private/macros/toolchains.bzl

@@ -11,8 +11,7 @@ def scala_toolchains(
         load_scala_toolchain_dependencies = True,
         fetch_sources = False,
         validate_scala_version = True,
-        scala_compiler_srcjars = {},
-        scala = True):
+        scala_compiler_srcjars = {}):
     """Instantiates @io_bazel_rules_scala_toolchains and all its dependencies.
 
     Provides a unified interface to configuring rules_scala both directly in a
@@ -52,24 +51,16 @@ def scala_toolchains(
             compiler srcjar metadata dictionaries containing:
             - exactly one "label", "url", or "urls" key
             - optional "integrity" or "sha256" keys
-        scala: whether to instantiate the core Scala toolchain
     """
-    num_toolchains = 0
+    scala_repositories(
+        maven_servers = maven_servers,
+        # Note the internal macro parameter misspells "overriden".
+        overriden_artifacts = overridden_artifacts,
+        load_dep_rules = load_rules_scala_dependencies,
+        load_jar_deps = load_scala_toolchain_dependencies,
+        fetch_sources = fetch_sources,
+        validate_scala_version = validate_scala_version,
+        scala_compiler_srcjars = scala_compiler_srcjars,
+    )
 
-    if scala:
-        num_toolchains += 1
-        scala_repositories(
-            maven_servers = maven_servers,
-            # Note the internal macro parameter misspells "overriden".
-            overriden_artifacts = overridden_artifacts,
-            load_dep_rules = load_rules_scala_dependencies,
-            load_jar_deps = load_scala_toolchain_dependencies,
-            fetch_sources = fetch_sources,
-            validate_scala_version = validate_scala_version,
-            scala_compiler_srcjars = scala_compiler_srcjars,
-        )
-
-    if num_toolchains != 0:
-        scala_toolchains_repo(
-            scala = scala,
-        )
+    scala_toolchains_repo()

scala/toolchains.bzl

@@ -1,12 +1,5 @@
-load("@io_bazel_rules_scala_config//:config.bzl", "SCALA_VERSIONS")
-load("@io_bazel_rules_scala//scala:scala_cross_version.bzl", "version_suffix")
-
 def scala_register_toolchains():
-    for scala_version in SCALA_VERSIONS:
-        native.register_toolchains(
-            "@io_bazel_rules_scala_toolchains//scala:toolchain" +
-            version_suffix(scala_version),
-        )
+    native.register_toolchains("@io_bazel_rules_scala_toolchains//...:all")
 
 def scala_register_unused_deps_toolchains():
     native.register_toolchains(